Liquid rheostat



Feb. 21, 1950 J. B. ROBERTSON LIQUID RHEOSTAT Filed Aug. 1, 1947 FIG. I.

I w W Insu/dfian INVENTOR N w 0 m m f Patented Feb. 21, 1950 LIQUID RHEOSTAT Jack B. Robertson, Seattle, Wash., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application August 1, 1947, Serial No. 765,283

3 Claims.

The present invention relates to rheostats in which the resistance is produced by a conducting element or elements and a liquid in contact therewith.

More specifically the rheostat is of the type wherein the resistance is determined by a conducting liquid in contact with a conductor or conductors, and variation of resistance is produced by changing the area of contact.

It is an object of the invention to provide a simple, easily constructed rheostat, of such a nature that it produces resistance changes in accordance with predetermined laws of variation.

The improved rheostat comprises a pair of electrodes with an interposed conducting liquid, constituting the resistance medium of the rheostat, and means for causing the liquid to escape at a controlled rate, thereby automatically varying the level of the liquid between the electrodes and consequently the resistance.

A further refinement comprises providing electrodes of special shapes, which in conjunction with the varying liquid level modify the rate of resistance change in accordance with a selected law of variation.

Other features of the invention include means whereby the progressive resistance changes may be repeated as often as may be desired, and the provision of duplicate apparatus whereby two rheostats may be mechanically connected in such a way that at any time only one of them is electrically active, while the other one simultaneously is being restored to its initial condition.

The invention will be understood clearly from the present specification and accompanying drawings, disclosing one specific example thereof.

In the drawings:

Figure 1 is a plan view of a preferred embodiment of the improved rheostat;

Figure 2 is a central vertical section thereof, on the plane indicated by line 2-2 of Figure 1 and looking in the direction of the arrows;

Figure 3 is a vertical section thereof on the plane indicated by line 33 of Figure 1; and

Figure 4 is a diagram illustrating one type of circuit in which the invention may be used.

Referring first to Figure 2, there is shown a supporting frame consisting of the two upright sides I 5, the base member I6 and the top member ll. It will be noted that the front and back of this frame are open, for a purpose that will appear presently. The frame is held together by the screws 28 and 29.

Approximately in the middle of each side panel I 5 is a pivot 9, adjustably held by nuts 25. The

inner ends of these pivots enter into holes 32 formed in bearing blocks 31, secured to the flange 38 of the separator 3 at diametrically opposite points by screws 30 and nuts 3|.

This separator 3, which has a circumferential flange 38, forms a partition between two vessels, and acts as the common bottom thereof. One of these vessels, the upper one, comprises a cylinder I located above the separator; the other, or lower one, has a similar cylinder I below the separator. The separator 3 and cylinder I are preferably made of Bakelite or some other material which combines the characteristics of being resistant to most electrolytes, strong, and not too brittle. The joints between the separator and the cylinders should be made liquid tight. This may be accomplished by the use of rubber cement or other suitable material, as indicated at 3a.

Each vessel is closed at its other end by a cap 2, likewise sealed to the cylinder I by use of suitable material such as a Neoprene washer or gasket l2. Into each cap 2 is threaded a screw 1, serving as a filler plug, with a Neoprene sealing washer l3 under its head. A tube 4 of Bakelite or the like in each vessel affords communication between them. These tubes 4 should likewise make liquid tight joints where they pass through the separator 3, as by means of rubber cement or other suitable sealing material.

The caps 2 are drawn together by means of the longitudinal rods 8. These pass through the flange 38 of the separator 3 and are held to the caps 2 by screws 22. This completes the mechanical structure.

The electrical elements associated with each vessel are the following:

Two plates or electrodes 5 are secured to each cap 2 by screws 2| and nuts 26. In order to make liquid-tight joints around these screws, washers I4, preferably of Neoprene, are provided. As shown, these electrodes 5 are parallel to one another, and spaced apart any suitable distance. To prevent play, the inner end of each electrode has a lug 33 projecting therefrom, these lugs fitting into slots 34 in a ring 6, of Bakelite or the like, set slidably into an annular depression 35 in the separator 3. Pins i8 secure the plates 5 to the rings 6. It will be noted that the rings do not reach the bottom of the holes 35, thereby allowing expansion or contraction of the electrodes to take place freely without causing any binding or breakage of the container.

0n the outer side of each cap 2 are arranged I two contact blades Ill, held by the same screws 55 2| that secure the electrodes 5. "Each blade in is thereby put into electrical connection with a corresponding electrode 5. The blades Ill have arcuate or curved ends as best shown in Figure 3. Each blade is bent at right angles adjacent the cap 2, to provide a flange to receive the screws. This flange also materially stiffens the blades.

The blades I may be considered as similar to the movable blades of a knife-switch in function. The co-acting stationary contacts are the spring clips I I carried by the top I! of the frame.

While it is possible to secure these assemblages of clips II and spacers I9 in place on the top I! in many different ways, a simple and preferred one is illustrated as providing angle supports secured to the top IT by the screws 2! and to the assemblages by the screws 23 which pass through the whole, nuts 36 serving to clamp all together. These screws 23 are also provided with knurled nuts 24 which serve to clamp Wires or other connections to the rheostat.

Referring now to Figure 4 there is shown an ex-' "ample of the use of the device. The base I6 and to tip even when the liquid is all in the upper vessel.

Having placed the desired amount of electrolyte in one of the vessels, this may be retained permanently by tightly closing the plugs l. Obviously only one vessel need have a filler opening and plug, but certain advantages in manufacture and use make it desirable to so equip both vessels. For example, the cover 2 will then be standardized, and whichever vessel is uppermost may be filled, whichever is down may be drained, and if either plug should become stuck,

the other will still be available.

Preferably an electrolyte will be chosen which has no deleterious eiTect on the plates 5, which may be made of beryllium-copper, and'the screws 21 and nuts 26, usually of brass. The seals afforded by the plugs also prevent the entrance of 'air or other gases into the electrolyte.

The electrical circuit, starting from the source 39, extends through the wire 4!], to one side of the electrical load 42, and returns to source 39 from the other side of the load through the wire M. A series resistor 44 may be placed in wire 40 or 4| and an additional resistor 43 may be placed in shunt to the rheostat as shown. Obviously the ohmic values of these devices will be selected to suit the use being made of the apparatus at any time, as will also the characteristics of the electrolyte.

Assuming that the top chamber 5 contains liquid, the latterwill flow into the lower chamber through the lower tube 4, while air will flow up through the other tube 4, to replace it. The submergence of the plates '5 inthe upper chamber will thus decrease at a rate "determined 'by the liquid head acting on the outlet tube, as well as the "flow resistance of said tube. As the liquid ,level recedes, the resistance between the two platestl will increase, smoothly and continuously, ibutnot'necessarily uniformly.

The flow of liquid is functionallyrelated to the circuits, as the case may be.

diflerence of pressure at the two ends of the outlet tube. Obviously this pressure difierence decreases as flow goes on, thus slowing down said flow. However, if the plates 5 are shaped appropriately, any desired rate of increase of resistance may be obtained. Thus, a low initial rate may be had by making the plates narrow at the top, and the reverse by making them narrow at the bottom, while special configurations will cause the resistance change to follow any desired law of variation.

While it is possible to make the plates 5 in one chamber difierent from those in the other, in order to have two diiierent rates with a single apparatus, on the whole it will be preferable to make the two chambers and contents identical, thus avoiding the possibility of mistakes and also saving time when the cycle of values is to be repeated, as it is necessary merely to invert the pivoted chambers when the new cycle is to begin,

without waiting'for the other chamber to'empty.

The shunt resistor 43 prevents complete open- 'ing of the circuit when the upper chamber becomes empty and may also serve other purposes, such as 15 set a maximum resistance which can not be exceeded, or to provide for a certain minimum of current, or to modify the action of the rheostat alone. The values of 33 and M accordingly will be made suitable for the specific work being done.

An example of the use of the invention would be the determination of electronic emission from a thermionic-tube cathode, such as a filament, in relation to the voltage or current applied. The voltage automatically will be varied continuously, and simultaneous readings or records of voltage and emission may be made. This may be repeated as often as desired with the same filament or with others, always giving the same time'rate of voltage or current variations, so that comparative results and checks may be secured easily and quickly. While the application to cathodes has been mentioned specifically, it willbe understood that the invention is not limited to any one field of use but is of general service whenever it is desired to produce automatically minimum value of resistance and increase this to the maximum during a run. This means that the current is highest at the start and is gradually decreased. v

If it is desired to start with a high resistance or a low current, the apparatus may be altered by merely adding a duplicate 'set of spring clips Ii at the lower end, that is, on the base plate It so that connections may be made to the electrodes 5 of the lowermost vessel l at will. Thisconnection will obviously give the desired result, since the liquid will accumulate in the lower chamber and thus progressively decrease the resistanceproduced in the apparatus.

Many other variations are possible, for example, both vessels may be used simultaneously, either inparts of the same circuit or in different Hence" theinvention is not to be construed as confined :totthe specific .:form illustrated, but is-defined solely by the following claims.

What is claimed is:

1. A rheostat comprising a base member, a pair of containers extending in opposite directions from said base member, individual pairs of electrodes of which one pair projects into each container, means establishing a passage for resistor liquid from one container to the other through said base and under the influence of gravity, means pivotally supporting said pair of containers about a horizontal axis whereby either may be turned to a position above the other, and a double pole double throw switch comprising two pairs of contacts carried by and movable with the containers and electrically connected to the respective electrodes, and a pair of stationary contacts designed and positioned to engage either movable pair, said switch thus being operated automatically by the pivotal shifting of the containers.

2. A rheostat comprising a vessel having therein a pair of closed compartments separated by a transverse partition, a liquid constituting an electrical resistor and confined by the compartments, means pivotally supporting the said vessel for rotation about a transverse axis, a pair of electrodes in each compartment and extending below the surface of said liquid, conduits within the compartments, and extending from said partition into the respective compartments to permit flow of the liquid from one compartment to the other, and means for establishing electrical contact between said electrodes and an external electrical circuit, said means comprising two pairs of movable switch contacts carried by the vessel and each connected to a respective pair of said electrodes, and a pair of stationary switch contacts, designed and positioned to engage either movable pair.

3. A rheostat comprising a closed vessel having an intermediate transverse partition dividing it into two compartments, two tubes each establishing communication from a location adjacent one side of said partition to a location adjacent the remote end of the opposite compartment, a quantity of liquid in said vessel, said liquid constituting the electrical resistance medium of the rheostat, a pair of electrodes in each compartment co-acting with said liquid, means for supporting said vessel so that either compartment may be placed above the other at will, and means establishing external electrical connections with the electrodes in said upper compartment, said means comprising two pairs of movable switch contacts carried by the vessel and each connected to a respective pair of said electrodes, and a pair of stationary switch contacts, designed and positioned to engage either movable pair.

JACK B. ROBERTSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 437,412 Deprez Sept. 30, 1890 1,023,602 Wallmann Apr. 16, 1912 1,323,176 Ebeling Nov. 25, 1919 1,691,984 Miller Nov. 20, 1928 

